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Abstract

State-of-the-art Fourier-domain optical coherence tomography (OCT) allows for the acquisition of up to millions of spectral fringes per second. This large amount of data can be used to improve the quality of structural tomograms after effective averaging. Here, we compare three OCT image improvement techniques: magnitude averaging, complex averaging, and spectral and time domain OCT (STdOCT). We evaluate the performance for images on both linear and logarithmic intensity scales and discuss their advantages and disadvantages. We propose the use of the STdOCT approach as it offers the best advantages. Applications to in vivo imaging and speckle reduction are presented.

Figures (10)

Schematic drawing of the tomogram line with parameters used to calculate the image quality metrics: m¯sand m¯b are the mean values of the signal and background magnitudes in the presence of noise, respectively, and σsand σb are the corresponding standard deviations.

STdOCT diagram indicating the order of procedures in data averaging for all three techniques. 1. Preprocessing (fixed-pattern noise reduction, resampling to wavenumber space, dispersion compensation). 2. Spatial Fourier transformation (FT) to in-depth position. 3. Magnitude or complex averaging. 3′. Temporal FT to Doppler frequency. 4′. Magnitude detection followed by information extraction in STdOCT processing. For each in-depth position, the signal with the maximum magnitude along the frequency axis is found. The magnitude value is used to create structural images, while the frequency value serves to create velocity maps.

Reflecting phantom experiment. PDFs and experimentally obtained histograms of the magnitudes of tomogram lines created with different averaging techniques for 8 averaged A-scans for a data set with s/σ=1.635. BCG−HIST: histogram of the background magnitudes; SIG−HIST: histogram of the signal magnitudes; BCG−PDF: theoretical PDF of the background magnitudes; and SIG−PDF: theoretical PDF of the signal magnitudes.

Reflecting phantom experiment. Image parameters calculated from the magnitudes of the tomogram lines as a function of the number of averaged A-scans for different averaging techniques of a data set with s/σ=1.635. Image parameters from left to right: m¯s: mean value of the signal; m¯b: mean value of the background noise; σs: standard deviation of the signal; and σb: standard deviation of the background noise.

(a). Images of the reflecting phantom for different averaging algorithms and number of averaged A-scans. Each tomogram is composed of 2 000 lines, and the dynamic range in all images is the same. Red rectangles indicate the regions of the tomograms used to calculate the image parameters in Fig. 6. For this data set, s/σ=1.635. (b). Tomogram lines before dynamic range equalization taken from the images shown in (a). To emphasize the difference in the dynamic range, all the lines have equal maximal signal values. Arrows show the position of the reflecting layer. MAG: magnitude averaging; STD: STdOCT averaging; and CPX: complex averaging.

Reflecting phantom experiment. Image quality metrics as a function of the number of averaged A-scans for different averaging techniques of a data set with s/σ=1.635. The intensity of the tomogram used for the calculation was equalized, which results in a constant dynamic range. C: speckle contrast; SNR: signal-to-noise ratio; DR: dynamic range; CNR: contrast-to-noise ratio; NOAVG: single A-scan; MAG: magnitude averaging; STD: STdOCT averaging; and CPX: complex averaging.

(a). Images of the uniform-scattering sample for different averaging algorithms and number of averaged A-scans. The effective lateral resolution is 14, 19, and 115 µm for N = 4, 16, and 256, respectively. The dynamic range in all images is equal. Red rectangles indicate the regions used to calculate the image parameters in Fig. 8. (b). Tomogram lines before dynamic range equalization of the images shown in (a). To emphasize the differences in the dynamic range, all the lines have equal maximal signal values. MAG: magnitude averaging; STD: STdOCT averaging; and CPX: complex averaging.

Scattering phantom experiment. Image quality metrics as a function of the number of averaged A-scans for different averaging techniques. The intensity of the tomogram used for the calculation of the parameters was equalized and results in a constant dynamic range. C: speckle contrast; SNR: signal-to-noise ratio; DR: dynamic range; CNR: contrast-to-noise ratio; NOAVG: single A-scan; MAG: magnitude averaging; STD: STdOCT averaging; and CPX: complex averaging.